Transparent eye drops containing latanoprost

ABSTRACT

An object of the present invention is to provide better formulations of a latanoprost ophthalmic solution. The present invention provides a clear ophthalmic solution comprising latanoprost as an active ingredient and benzalkonium chloride as a preservative wherein white turbidity due to a change of formulation is prevented by at least one means selected from the following 1) to 3); 1) adding a surfactant, 2) using benzalkonium chloride represented by the formula of [C 6 H 5 CH 2 N(CH 3 ) 2 R]Cl (wherein R is alkyl having 12 carbon atoms) as the preservative and 3) adding a nonionic tonicity agent as a tonicity agent.

This application is the United States national phase application ofInternational Application PCT/JP2003/11402 filed Sep. 8, 2003.

TECHNICAL FIELD

The present invention relates to a clear and stable ophthalmic solutioncomprising latanoprost, which is useful as a therapeutic agent forglaucoma, as an active ingredient.

BACKGROUND ART

Latanoprost is a prostaglandin-type therapeutic agent for glaucomarepresented by a chemical name of isopropyl(Z)-7[(1R,2R,3R,5S)3,5-dihydroxy-2-[(3R)-3-hydroxy-5-phenylpentyl]cyclopentyl]-5-heptanoate.Latanoprost is a selective FP receptor agonist and lowers intraocularpressure by promoting outflow of an aqueous humor (See, for example,Japanese Patent No. 2721414). An administration route of latanoprost isinstillation, and an ophthalmic solution containing 0.005% latanoprost(trade name: Xalatan ophthalmic solution) is commercially available.

An object of the present invention is to provide better formulations ofa latanoprost ophthalmic solution.

As a preservative of the ophthalmic solution, benzalkonium chloride(hereinafter abbreviated as “BAK”) is the most widely used from thestandpoint of effects and the like. However, while BAK has an excellentpreservative effect, BAK may cause corneal disorders when it is used ata high concentration. Accordingly, when BAK is added to the ophthalmicsolution, it is desirable to lower its concentration as low as possible.

BAK described in the specification means a mixture of compounds having achemical structure represented by [C₆H₅CH₂N(CH₃)₂R]Cl wherein alkyl(represented by R) is C₈H₁₇˜C₁₈H₃₇.

BAK is defined as follows in Japanese, United States and EuropeanPharmacopoeia.

Japanese Pharmacopoeia: BAK is represented by [C₆H₅CH₂N(CH₃)₂R]Clwherein R is C₈H₁₇˜C₁₈H₃₇ and mainly comprises C₁₂H₂₅ and C₁₄H₂₉.

United States Pharmacopoeia: BAK is a mixture ofalkylbenzyldimethylammonium chloride represented by [C₆H₅CH₂N(CH₃)₂R]Clwherein R is a mixture of all or some alkyl groups which are higher thanC₈H₁₇ and mainly comprises C₁₂H₂₅, C₁₄H₂₉ and C₁₆H₃₃.

European Pharmacopoeia: BAK is a mixture of alkylbenzyldimethylammoniumchloride wherein alkyl has chain length of C₈ to C₁₈.

On the other hand, a tonicity agent is usually added to the ophthalmicsolution in order to keep isotonicity and is exemplified by inorganicsalts such as alkali metal salts such as sodium chloride and alkalineearth metal salts such as magnesium chloride.

Further, a buffer is usually added to the ophthalmic solution in orderto prevent a change of pH and is exemplified by inorganic salts such assodium phosphate and sodium borate and organic salts such as sodiumacetate, sodium citrate and sodium carbonate.

The tonicity agent and the buffer are contained in a commerciallyavailable latanoprost ophthalmic solution.

The present inventors prepared and studied latanoprost ophthalmicsolutions containing these widely-used additives.

As a result, surprisingly it was turned out that white turbidity is notobserved at a BAK concentration of 0.015% or higher, while it isobserved at a BAK concentration of 0.01% or lower. That is becausehydrophobic latanoprost and BAK form a complex, and the latanoprost-BAKcomplex is precipitated due to a salting-out effect by salts, i.e.additives. The present inventors discovered the fact, to their surprise,that the complex is not precipitated until the BAK concentration islowered to 0.01% or lower. Since the commercially available latanoprostophthalmic solution (trade name: Xalatan ophthalmic solution) contains0.02% of BAK, a problem of white turbidity is not caused. However, asmentioned above, though BAK is the excellent preservative, it may causethe corneal disorders when used at the high concentration. Accordingly,when BAK is added to the ophthalmic solution, it is desirable to lowerits concentration as low as possible.

DISCLOSURE OF THE INVENTION

First studying various additives for preventing white turbidity, thepresent inventors found that white turbidity can be prevented by addinga surfactant.

Carrying out intensive studies by focusing attention on the kind of BAK,it was found that white turbidity can be prevented not by using amixture of compounds represented by the above chemical structuralformula wherein alkyl has 8 to 18 carbon atoms but by using BAK in whichalkyl has 12 carbon atoms.

Further, the present inventors considered that use of salts as tonicityagents may be a cause of white turbidity and carried out precise studiesfocusing attention on the kind of tonicity agent. As a result, it wasfound that white turbidity can be prevented by using nonionic tonicityagents as tonicity agents.

Namely, it was found that a clear ophthalmic solution comprisinglatanoprost as an active ingredient and benzalkonium chloride as apreservative, wherein white turbidity due to a change of formulation isprevented by at least one means selected from the following 1) to 3), isobtained;

-   1) adding a surfactant,-   2) using benzalkonium chloride represented by the formula of    [C₆H₅CH₂N(CH₃)₂R]Cl (wherein R is alkyl having 12 carbon atoms) as    the preservative and-   3) adding a nonionic tonicity agent as a tonicity agent.

The above-mentioned three means can be used solely or in combination.

A concentration of latanoprost, which is the active ingredient of theophthalmic solution in the present invention, is preferably 0.001 to0.01% (W/V), particularly preferably 0.005% (W/V).

The first means in the present invention is adding a surfactant. Whenthe surfactant is added, the clear latanoprost ophthalmic solutionwherein white turbidity is prevented can be obtained independently ofthe kind of tonicity agent and the kind of BAK.

Examples of surfactants are Polysorbate 80, polyoxyethylene hydrogenatedcastor oil 60, polyoxyl 35 castor oil, polyethylene glycol monostearate,macrogol 4000, lecithin, sucrose ester, polyoxyethylene alkyl ether,polyoxyl stearate, polyoxyethylene polyoxypropylene glycol and the like,preferably Polysorbate 80, polyoxyethylene hydrogenated castor oil 60and polyoxyl 35 castor oil. A concentration of the surfactant ispreferably 0.001 to 0.5%.

The second means in the present invention is using benzalkonium chloriderepresented by the formula of [C₆H₅CH₂N(CH₃)₂R]Cl (wherein R is alkylhaving 12 carbon atoms) as a preservative. Benzalkonium chloride whereinalkyl has 12 carbon atoms described in the specification (hereinafterabbreviated as “BAK-C₁₂”) means benzalkonium chloride which has achemical structure represented by [C₆H₅CH₂N(CH₃)₂R]Cl and whose alkyl(represented by R in the formula) is C₁₂H₂₅.

The clear latanoprost ophthalmic solution wherein white turbidity isprevented can be obtained independently of the kind of tonicity agent byusing BAK-C₁₂ as a preservative.

Commercially available BAK-C₁₂ can be used. A concentration of BAK-C₁₂is preferably 0.01% (W/V) or lower. When the BAK concentration is toolow, the sufficient preservative effect is not exhibited. Accordingly, amore preferred BAK concentration is in the range of 0.003 to 0.01%(W/V).

The third means in the present invention is adding a nonionic tonicityagent as a tonicity agent. The clear latanoprost ophthalmic solutionwherein white turbidity is prevented can be obtained independently ofthe kind of BAK by using the nonionic tonicity agent. When the nonionictonicity agent is used, a total amount of salts in the ophthalmicsolution can be reduced. As a result, an influence of a salting-outeffect is decreased, and thereby white turbidity is prevented.

The nonionic tonicity agents can be any agents to be usually used forophthalmic solutions and are specifically exemplified by glycerin,mannitol, polyethylene glycol, propylene glycol, trehalose, sucrose andthe like. A concentration of the nonionic tonicity agent is adjusted toa concentration which can be isotonic for each substance.

The ophthalmic solution of the present invention can be preparedoptionally by adding a pH buffer, a pH adjusting agent, a solubilizer ora viscous agent. Examples of pH buffers are phosphates such as sodiumphosphate, sodium dihydrogenphosphate, disodium

hydrogenphosphate, potassium phosphate, potassium dihydrogenphosphateand dipotassium

hydrogenphosphate; borates such as sodium borate and potassium borate;citrates such as sodium citrate and disodium citrate; acetates such assodium acetate and potassium acetate; and carbonates such as sodiumcarbonate and sodium hydrogencarbonate. Examples of pH adjusting agentsare hydrochloric acid, citric acid, phosphoric acid, acetic acid, sodiumhydroxide, potassium hydroxide and the like. Examples of solubilizersare Polysorbate 80, polyoxyethylene hydrogenated castor oil 60, macrogol4000 and the like. Examples of viscous agents arehydroxypropylmethylcellulose,

-   hydroxypropylcellulose,-   polyvinyl alcohol, carboxyvinyl polymer,-   polyvinylpyrrolidone and the like.

A salt such as sodium chloride, potassium chloride calcium chloride ormagnesium chloride can be added as the tonicity agent in the means 1 and2.

pH of the ophthalmic solution of the present invention is preferablyadjusted to 3 to 8, more preferably 4 to 7.

The ophthalmic solution of the present invention can be prepared bywidely-used processes.

BEST MODE FOR CARRYING OUT THE INVENTION Examples According to Means 1)Example 1-1

Crystalline sodium dihydrogenphosphate (0.2 g), sodium chloride (0.8 g),Polysorbate 80 (0.01 g) and benzalkonium chloride (0.01 g) weredissolved in purified water (approximately 90 ml), pH was adjusted to6.7, and purified water was added to the solution so that total volumewas 100 ml to give a vehicle. The vehicle (100 ml) was added tolatanoprost (5 mg), and the mixture was stirred while warming it in awater bath at about 80° C. to dissolve latanoprost in the vehicle. Thetemperature of the solution was returned to room temperature, and thenpH was confirmed to be 6.7.

Example 1-2

Crystalline sodium dihydrogenphosphate (0.2 g), sodium chloride (0.8 g),polyoxyethylene hydrogenated castor oil 60 (0.01 g) and benzalkoniumchloride (0.01 g) were dissolved in purified water (approximately 90ml), pH was adjusted to 6.7, and purified water was added to thesolution so that total volume was 100 ml to give a vehicle. The vehicle(100 ml) was added to latanoprost (5 mg), and the mixture was stirredwhile warming it in a water bath at about 80° C. to dissolve latanoprostin the vehicle. The temperature of the solution was returned to roomtemperature, and then pH was confirmed to be 6.7.

Example 1-3

Crystalline sodium dihydrogenphosphate (0.2 g), sodium chloride (0.8 g),polyoxyl 35 castor oil 60 (0.01 g) and benzalkonium chloride (0.01 g)were dissolved in purified water (approximately 90 ml), pH was adjustedto 6.7, and purified water was added to the solution so that totalvolume was 100 ml to give a vehicle. The vehicle (100 ml) was added tolatanoprost (5 mg), and the mixture was stirred while warming it in awater bath at about 80° C. to dissolve latanoprost in the vehicle. Thetemperature of the solution was returned to room temperature, and thenpH was confirmed to be 6.7.

Examples According to Means 2) Example 2-1

Crystalline sodium dihydrogenphosphate (0.2 g), sodium chloride (0.8 g)and BAK-C₁₂ (0.01 g) were dissolved in purified water (approximately 90ml), pH was adjusted to 6.7 with a 1 N aqueous sodium hydroxidesolution, and purified water was added to the mixture so that totalvolume was 100 ml to give a vehicle. The vehicle (100 ml) was added tolatanoprost (5 mg), and the mixture was stirred while warming it in awater bath at about 80° C. to dissolve latanoprost in the vehicle. Thetemperature of the solution was returned to room temperature, and thenpH was confirmed to be 6.7.

Example 2-2

Crystalline sodium dihydrogenphosphate (0.2 g), sodium chloride (0.8 g)and BAK-C₁₂ (0.005 g) were dissolved in purified water (approximately 90ml), pH was adjusted to 6.7 with a 1 N aqueous sodium hydroxidesolution, and purified water was added to the mixture so that totalvolume was 100 ml to give a vehicle. The vehicle (100 ml) was added tolatanoprost (5 mg), and the mixture was stirred while warming it in awater bath at about 80° C. to dissolve latanoprost in the vehicle. Thetemperature of the solution was returned to room temperature, and thenpH was confirmed to be 6.7.

Examples According to Means 3) Example 3-1

Crystalline sodium dihydrogenphosphate (0.2 g), concentrated glycerin(2.3 g) and BAK (0.01 g) were dissolved in purified water (approximately90 ml), pH was adjusted to 6.7 with a 1 N aqueous sodium hydroxidesolution, and purified water was added to the mixture so that totalvolume was 100 ml to give a vehicle. The vehicle (100 ml) was added tolatanoprost (5 mg), and the mixture was stirred while warming it in awater bath at about 80° C. to dissolve latanoprost in the vehicle. Thetemperature of the solution was returned to room temperature, and thenpH was confirmed to be 6.7.

Example 3-2

Crystalline sodium dihydrogenphosphate (0.2 g), mannitol (4.5 g) and BAK(0.01 g) were dissolved in purified water (approximately 90 ml), pH wasadjusted to 6.7 with a 1 N aqueous sodium hydroxide solution, andpurified water was added to the mixture so that total volume was 100 mlto give a vehicle. The vehicle (100 ml) was added to latanoprost (5 mg),and the mixture was stirred while warming it in a water bath at about80° C. to dissolve latanoprost in the vehicle. The temperature of thesolution was returned to room temperature, and then pH was confirmed tobe 6.7.

Example 3-3

Crystalline sodium dihydrogenphosphate (0.2 g), polyethylene glycol 400(8.0 g) and BAK (0.01 g) were dissolved in purified water (approximately90 ml), pH was adjusted to 6.7 with a 1 N aqueous sodium hydroxidesolution, and purified water was added to the mixture so that totalvolume was 100 ml to give a vehicle. The vehicle (100 ml) was added tolatanoprost (5 mg), and the mixture was stirred while warming it in awater bath at about 80° C. to dissolve latanoprost in the vehicle. Thetemperature of the solution was returned to room temperature, and thenpH was confirmed to be 6.7.

Example 3-4

Crystalline sodium dihydrogenphosphate (0.2 g), propylene glycol (2.0 g)and BAK (0.01 g) were dissolved in purified water (approximately 90 ml),pH was adjusted to 6.7 with a 1 N aqueous sodium hydroxide solution, andpurified water was added to the mixture so that total volume was 100 mlto give a vehicle. The vehicle (100 ml) was added to latanoprost (5 mg),and the mixture was stirred while warming it in a water bath at about80° C. to dissolve latanoprost in the vehicle. The temperature of thesolution was returned to room temperature, and then pH was confirmed tobe 6.7.

Example 3-5

Crystalline sodium dihydrogenphosphate (0.2 g), trehalose (9.0 g) andBAK (0.01 g) were dissolved in purified water (approximately 90 ml), pHwas adjusted to 6.7 with a 1 N aqueous sodium hydroxide solution, andpurified water was added to the mixture so that total volume was 100 mlto give a vehicle. The vehicle (100 ml) was added to latanoprost (5 mg),and the mixture was stirred while warming it in a water bath at about80° C. to dissolve latanoprost in the vehicle. The temperature of thesolution was returned to room temperature, and then pH was confirmed tobe 6.7.

Experiment 1: Measurement of Residual Ratio of Latanoprost andObservation of Appearance

1) Comparative formulations 1 to 4 were prepared as follows.

Purified water (approximately 90 ml) was placed in a 100 ml-glassbeaker. Crystalline sodium dihydrogenphosphate (0.2 g) and sodiumchloride (0.9 g) were dissolved in the purified water, pH was adjustedto 6.7 with a 1 N aqueous sodium hydroxide solution, and purified waterwas added to the mixture so that total volume was 100 ml to give avehicle. The vehicle (100 ml) was added to latanoprost (5 mg), and themixture was stirred while warming it in a water bath at about 80° C. todissolve latanoprost in the vehicle. The temperature of the solution wasreturned to room temperature, and then pH was confirmed to be 6.7. Waterfor injection was added to the solution to adjust total volume to 100ml. In a glass test tube was placed precisely 10 ml of the latanoprostsolution, 50, 100, 150 or 200 μl of a 1% BAK (a mixture of compoundshaving 12, 14 and 16 carbon atoms of alkyl R in the above chemicalstructural formula) solution was added thereto, and they were mixed.These formulations are shown in Table 1.

2) Formulations 1 to 3 were prepared as follows.

Purified water (approximately 90 ml) was placed in a 100 ml-glassbeaker. Crystalline sodium dihydrogenphosphate (0.2 g), sodium chloride(0.9 g) and each surfactant were dissolved in the purified water so thateach concentration was the value shown in Table 2, pH was adjusted to6.7 with an aqueous sodium hydroxide solution or diluted hydrochloricacid, and purified water was added to the mixture so that total volumewas 100 ml to give a vehicle. The vehicle (100 ml) was added tolatanoprost (5 mg), and the mixture was stirred while warming it in awater bath at about 80° C. to dissolve latanoprost in the vehicle. Thetemperature of the solution was returned to room temperature, and thenpH was confirmed to be 6.7. Water for injection was added to thesolution to adjust total volume to 100 ml. In a glass test tube wasplaced precisely 10 ml of the latanoprost solution, 100 μl of a 1% BAK(a mixture of compounds having 12, 14 and 16 carbon atoms of alkyl R inthe above chemical structural formula) solution was added thereto, andthey were mixed. These formulations are shown in Table 2.

3) Formulations 4 and 5 were prepared as follows.

Purified water (approximately 90 ml) was placed in a 100 ml-glassbeaker. Crystalline sodium dihydrogenphosphate (0.2 g) and sodiumchloride (0.9 g) were dissolved in the purified water, pH was adjustedto 6.7 with a 1 N aqueous sodium hydroxide solution, and purified waterwas added to the mixture so that total volume was 10.0 ml to give avehicle. The vehicle (100 ml) was added to latanoprost (5 mg), and themixture was stirred while warming it in a water bath at about 80° C. todissolve latanoprost in the vehicle. The temperature of the solution wasreturned to room temperature, and then pH was confirmed to be 6.7. Waterfor injection was added to the solution to adjust total volume to 100ml. In a glass test tube was placed precisely 10 ml of the latanoprostsolution, 50 or 100 μl of a 1% BAK-C₁₂ solution was added thereto, andthey were mixed. These formulations are shown in Table 3.

4) Formulations 6 to 10 were prepared as follows.

Purified water (approximately 90 ml) was placed in a 100 ml-glassbeaker. Crystalline sodium dihydrogenphosphate (0.2 g) and each nonionictonicity agent were dissolved in the purified water so that eachconcentration was the value shown in Table 4, pH was adjusted to 6.7with an aqueous sodium hydroxide solution or diluted hydrochloric acid,and purified water was added to the mixture so that total volume was 100ml to give a vehicle. The vehicle (100 ml) was added to latanoprost (5mg), and the mixture was stirred while warming it in a water bath atabout 80° C. to dissolve latanoprost in the vehicle. The temperature ofthe solution was returned to room temperature, and then pH was confirmedto be 6.7. Water for injection was added to the solution to adjust totalvolume to 100 ml. Into a glass test tube was placed precisely 10 ml ofthe latanoprost solution, 100 μl of a 1% BAK (a mixture of compoundshaving 12, 14 and 16 carbon atoms of alkyl R in the above chemicalstructural formula) solution was added thereto, and they were mixed.These formulations are shown in Table 4.

5) Appearance of each solution prepared by the above-mentioned methodwas observed, and precisely 1 ml of each solution was sampled in a 25-mlmessflask. Nine milliliters of each remaining solution were filteredwith a 0.2-μm filter.

6) Latanoprost concentrations in the solutions were measured before andafter filtration by high performance liquid chromatography, and residualratios were calculated.

TABLE 1 Compara- Compara- Compara- Compara- tive tive tive tive formula-formula- formula- formula- tion 1 tion 2 tion 3 tion 4 Latanoprost 0.0050.005 0.005 0.005 Crystalline sodium 0.2 0.2 0.2 0.2 dihydrogenphosphateSodium chloride 0.9 0.9 0.9 0.9 BAK 0.02 0.015 0.01 0.005 Dilutedhydrochloric q.s. q.s. q.s. q.s. acid Sodium hydroxide q.s. q.s. q.s.q.s. Purified water q.s. q.s. q.s. q.s. (Unit in Table: % (W/V), q.s.:quantum sufficient)

TABLE 2 Formulation 1 Formulation 2 Formulation 3 Latanoprost 0.0050.005 0.005 Crystalline sodium 0.2 0.2 0.2 dihydrogenphosphate Sodiumchloride 0.9 0.9 0.9 BAK 0.01 0.01 0.01 Polysorbate 80 0.01 — —Polyoxyethylene — 0.01 — hydrogenated castor oil 60 Polyoxyl 35 castoroil — — 0.01 Diluted hydrochloric q.s. q.s. q.s. acid Sodium hydroxideq.s. q.s. q.s. Purified water q.s. q.s. q.s. (Unit in Table: % (W/V),q.s.: quantum sufficient)

TABLE 3 Formulation 4 Formulation 5 Latanoprost 0.005 0.005 Crystallinesodium 0.2 0.2 dihydrogenphosphate Sodium chloride 0.9 0.9 BAK C-₁₂ 0.010.005 Diluted hydrochloric acid q.s. q.s. Sodium hydroxide q.s. q.s.Purified water q.s. q.s. (Unit in Table: % (W/V), q.s.: quantumsufficient)

TABLE 4 Formulation Formulation Formulation Formulation Formulation 6 78 9 10 Latanoprost 0.005 0.005 0.005 0.005 0.005 Crystalline sodium 0.20.2 0.2 0.2 0.2 dihydrogenphosphate BAK 0.01 0.01 0.01 0.01 0.01Concentrated glycerin 2.5 — — — 13 Mannitol — 5 — — — PEG 400 — — 8.5 —— Propylene glycol — — — 2.1 — Trehalose — — — — 9.25 Dilutedhydrochloric q.s. q.s. q.s. q.s. q.s. acid Sodium hydroxide q.s. q.s.q.s. q.s. q.s. Purified water q.s. q.s. q.s. q.s. q.s. (Unit in Table: %(W/V), q.s.: quantum sufficient)Results

Table 5 shows results of appearance observation and residual ratiomeasurement of comparative formulations 1 to 4. In comparativeformulations 1 and 2 containing 0.02% or 0.015% of BAK added tolatanoprost, appearance was colorless and transparent, and residualratios were 96.8 to 99.4%. That is to say, the formulations did notchange. However, in comparative formulations 3 and 4 containing 0.01% or0.005% of BAK, white turbidity was observed, and residual ratiosdecreased. That is to say, the formulations changed.

Table 6 shows results of appearance observation and residual ratiomeasurement of formulations 1 to 3 (means 1). In comparativeformulations 3 and 4, white turbidity was observed, and the residualratios decreased. To the contrary, in formulations 1 to 3 containing thesurfactant, white turbidity was not observed, and residual ratios kepthigh values, i.e., 97.2 to 99.8%. These results show that when thesurfactant is added to the formulations comprising latanoprost and BAK,the surfactant prevents the formulation from changing, and therebystable and clear ophthalmic solutions are obtained.

Table 7 shows results of appearance observation and residual ratiomeasurement of formulations 4 and 5 (means 2). In comparativeformulations 3 and 4 using BAK, white turbidity was observed, and theresidual ratios decreased. To the contrary, in formulations 4 and 5containing BAK-C₁₂ instead of BAK, white turbidity was not observed, andresidual ratios were 97.3 to 98.2%. That is to say, the formulations didnot change. These results show that when BAK-C₁₂ is added instead of BAKto the formulation comprising latanoprost, BAK-C₁₂ prevents theformulation from changing, and thereby stable and clear ophthalmicsolutions are obtained.

Table 8 shows results of appearance observation and residual ratiomeasurement of formulations 6 to 10. In comparative formulations 3 and 4containing sodium chloride as the tonicity agent, white turbidity wasobserved, and the residual ratios decreased. To the contrary, informulations 6 to 10 containing the nonionic tonicity agent instead ofsodium chloride, white turbidity was not observed, and residual ratioswere 94.6 to 98.6%. That is to say, the formulations did not change.These results show that when the nonionic tonicity agent is added as atonicity agent to the formulations comprising latanoprost and BAK, theagent prevents the formulation from changing, and thereby stable andclear ophthalmic solutions are obtained.

TABLE 5 Comparative Comparative Comparative Comparative formula-formula- formula- formula- tion 1 tion 2 tion 3 tion 4 Appear- Colorlessand Colorless and White White ance transparent transparent turbidityturbidity Residual 99.4 96.8 67.3 83.5 ratio (%)

TABLE 6 Formulation 1 Formulation 2 Formulation 3 Appearance Colorlessand Colorless and Colorless and transparent transparent transparentResidual 99.8 98.0 97.2 ratio (%)

TABLE 7 Formulation 4 Formulation 5 Appearance Colorless and Colorlessand transparent transparent Residual ratio (%) 97.3 98.2

TABLE 8 Formulation 6 Formulation 7 Formulation 8 Formulation 9Formulation 10 Appearance Colorless and Colorless and Colorless andColorless and Colorless and transparent transparent transparenttransparent transparent Residual 98.6 96.0 94.6 98.2 96.2 ratio (%)

Experiment 2: Antimicrobial Effectiveness Tests

Antimicrobial effectiveness tests were carried out for theabove-mentioned Examples 1-1, 2-1 and 3-1, according to theantimicrobial effectiveness test method described in the 13th revisedJapanese Pharmacopoeia.

Test results are shown in Table 9. In the case of bacteria, after fourweeks from inoculation, the bacteria was not detected in any Examples.In the case of fungus, after four weeks from inoculation, the fungus wasnot detected or the number was remarkably fewer than that of inoculatedfungus. Accordingly, the preservative effect was found to besufficiently exhibited.

TABLE 9 Microbe number after four Microbe weeks number on ExampleExample Example innoculation 1-1 2-1 3-1 Bacteria E.coli 1.4 × 10⁶ NotNot Not detected detected detected P. 8.9 × 10⁶ Not Not Not areruginosadetected detected detected S.aureus 2.2 × 10⁶ Not Not Not detecteddetected detected Fungus C.albicans 8.2 × 10⁶ Not Not 1.1 × 10³ detecteddetected A.niger 9.0 × 10⁶ Not 10 or Not detected fewer detected

INDUSTRIAL APPLICABILITY

By adding a surfactant, clear latanoprost ophthalmic solutions can beprovided even if a BAK concentration is lowered. In addition, by usingBAK-C₁₂ as a preservative, clear latanoprost ophthalmic solutions can beprovided even if the BAK concentration is lowered, too. Further, byadding a nonionic tonicity agent, clear latanoprost ophthalmic solutionscan be also provided even if the BAK concentration is lowered.

1. A clear ophthalmic solution comprising (i) latanoprost having aconcentration of 0.005% (W/V), (ii) 0.003 to 0.01% (W/V) of benzalkoniumchloride represented by the formula of [C₆H₅CH₂N(CH₃)₂R]C1, wherein R isan alkyl group having 12 carbon atoms and (iii) at least onepharmaceutically acceptable carrier selected from the group consistingof crystalline sodium dihydrogenphosphate sodium chloride, dilutedhydrochloric acid and sodium hydroxide.
 2. A method of preventing whiteturbidity in an ophthalmic solution comprising latanoprost having aconcentration of 0.005% (WV) and at least one pharmaceuticallyacceptable carrier selected from the group consisting of crystallinesodium dihydrogenphosphate, sodium chloride, diluted hydrochloric acidand sodium hydrogen, the method comprising adding to said solution 0.003to 0.01% (W/V) benzalkonium chloride represented by the formula[C₆H₅CH₂N(CH₃)₂R]C1, wherein R is an alkyl group having 12 carbon atoms.